This disclosure relates to mechanical power transmissions in general, and in particular, to compact, reduced weight and complexity, split torque, geared power transmission having composite output shafts for reduced weight.
The applications in which relatively large amounts of power need to be transmitted from one or more driving mechanisms, e.g., rotating turbines or engines, to a driven element, e.g., the tracks of a tank, the screw of a ship or submarine, or the main rotor of a helicopter, are legion. The problem with existing geared power transmissions is their relatively high weight-to-power transmission ratios. That is, as the amount of power that needs to be transmitted from the driving mechanism(s) to the driven mechanism(s) increases, the size and weight of the gears and supports in the transmission increase disproportionately. In some applications, e.g., hydroelectric power generating stations or ships, this increase in weight and size can be accommodated relatively easily, whereas, in others, e.g., aircraft and rotorcraft, the increased weight, size and complexity can severely compromise vehicle design and performance.
In an effort to address this problem, a number of so-called “split torque” geared power transmissions have been developed over the years. Examples of geared transmissions adapted to apply multiple torques from one or more relatively high-speed engines to a single, slower turning helicopter main rotor can be found in, e.g., U.S. Pat. Nos. 4,489,625 to G. White and 6,428,443 to L. Dischler. These prior solutions provide very limited reduction in weight because they utilize relatively large numbers of gears that require numerous, heavy gearing supports.
What is needed then is a simple, light weight split torque geared transmission that is capable of transmitting higher torques, but which has a reduced weight that is achieved by a reduction in the number of gears and support bearings required for the gears, together with the utilization of low weight, high strength composite materials.